Liquids, such as crude oil, condensate and water, produced from wells typically contain gasses such as natural gas and liquid petroleum gas (LPG). Large amounts of oil, condensate and water that are produced are stored in storage tanks, awaiting transport, further processing or refining. When liquid is stored in a storage tank, gas contained in the liquid can separate or vaporize due to a variety of factors. For example, if the liquid experiences a pressure drop, then vapors will flash off. If the liquid level in the storage tank changes, or the liquid is agitated, the gas separates. If the tank is subjected to temperature swings or barometric pressure changes, gas can also separate from the liquid.
Due to environmental and economic reasons, it is desirable to capture these gasses. Capturing the gasses allows the gas to be sold. Alternatively, the gas can be burned. Venting the gas into the atmosphere is generally frowned upon and in most cases is restricted or requires permits.
Furthermore, providing liquid with gasses that can vaporize into a storage tank results in pressure changes inside the tank. As the pressure changes, atmospheric air may be drawn into the storage tank. Oil equipment operators, and in particular pipeline operators, do not want atmospheric air, with oxygen, introduced into their equipment due to problems with corrosion.
Thus, it is desirable to put so called “dead” oil, without gasses, (and other degassed liquids) into storage tanks. Dead oil does not produce gas inside of a storage tank, even when subjected to agitation, pressure drops, or temperature changes.
In the prior art, various types of equipment exists to separate and capture gas from liquid before the liquid is provided to a storage tank. One such type of equipment is known as a vapor recovery tower (VRT). The vapor recovery tower separates the gas from liquid in such a manner so as not to introduce air into the storage tank.
The prior art vapor recovery tower, while removing much of the gas from the liquid, is not particularly efficient in that significant quantities of gas can still be provided to the liquid flowing into a storage tank.
It is desired to provide a more efficient vapor recovery tower and method.